The present invention relates to monitoring of semiconductor processes. More particularly, the present invention relates to a method and system for monitoring characteristics of films exposed to a plasma in a semiconductor processing chamber.
Process control and diagnostics are important to determine the characteristics of films being deposited during semiconductor processing. For example, current process control and diagnostics of plasma enhanced deposition processes involve three techniques: optical endpoint detection, interferometric endpoint detection and test substrate measurement technique. The optical endpoint detection technique involves ascertaining a process endpoint by monitoring one or two narrow bands of optical emission from process plasmas. A drawback with this technique concerns the limited information regarding the characteristics of the films being deposited.
The interferometric endpoint technique takes advantage of interferometry to determine whether a film has obtained a predetermined thickness. Drawbacks associated with the interferometric endpoint technique include the limitations of materials that are suitable for use with interferometric measurements. Some materials, such as metals, do not show interferometric interference fringes unless the material being measured is extremely thin. Secondly, the interferometric technique does not predict true process endpoints.
The test substrate measurement technique involves direct measurement of a film disposed on a substrate. As a result, the test substrate measurement technique evaluates the last process step performed by examination of test wafers that are processed within a group of production wafers. This is a drawback, because this technique does not identify failures of intermediate process steps. This may result in the loss of a great number of process wafers. In addition, the test substrate measurement technique is destructive in nature, substantially reducing the operational life of the test substrate.
What is needed, therefore, is a non-destructive technique to monitor process conditions in a semiconductor processing chamber in real-time that accurately characterize films being deposited on a substrate.
Provided is a method and system that features monitoring characteristics of films by sensing the spectral emissions of a plasma to which the films are exposed. As a result, the method includes sensing optical energy produced by the plasma. The optical energy has a plurality of spectral bands associated therewith, a subset of which is identified as including information corresponding to the film characteristics. The film characteristics are then measured as a function of thaws information. Specifically, the intensity of the subset of spectral bands is sensed from which the film characteristics are determined. To increase the accuracy of the measurements, in one embodiment of the present invention a subgroup of the plurality of spectral bands is observed that has data associated therewith that is substantially independent of the characteristics of interest. In this manner, film characteristics are measured as a function of both the information and the data. Specifically, the intensity of the spectral bands associated with the subset and subgroup are identified and quantized, defining first and second quantizations. A ratio of the first and second quantizations is determined that attenuates information that results from degradation of the processing environment. The system includes a detector in optical communication with the processing chamber to sense optical energy generated by the plasma, and a spectrum analyzer, in electrical communication with the optical detector. The spectrum analyzer resolves the spectral bands and produces information corresponding thereto. A processor is in electrical communication with the spectrum analyzer, and a memory is in electrical communication with the processor. The memory includes a computer-readable medium having a computer-readable program embodied therein that controls the system to carry-out the method.